INTRODUCTION TO GRAPHS

First, a coördinate. A coördinate is a number. It labels a point on a line.

The coördinates 0, 1, 2, 3, etc. label those points. They are the "addresses" of those points.

A coördinate axis is a line with coördinates.

To label the points in a plane, we will need more than one coördinate axis, and we place them at right angles. Hence, they are called rectangular coördinate axes. And the coördinates on them are called rectangular coördinates. They are also called Cartesian coördinates, after the 17th century philosopher and mathematician René Descartes, for he was one of the first to exploit the geometrical possibilities of coördinates.

Finally, the rectangular coördinates of a point are an ordered pair, (x, y). (2, 3) labels a different point than (3, 2). The x-coördinate is always entered first, and the
y-coördinate second.